Our ongoing work focuses on the immunomodulatory properties of eosinophils, notably: Our original publication focuses on a unique subset of eosinophils identified in the lungs of allergen-challenged wild-type and gene-deleted mice. In this publication, we characterized an eosinophil subpopulation defined by high levels of expression of the neutrophil antigen Gr1 (CD45+CD11c-SiglecF+Gr1hi). SiglecF+Gr1hi eosinophils, distinct from the canonical SiglecF+Gr1- eosinophil population, were detected in allergen-challenged wild-type and granule protein deficient (EPX-/- and MBP-1-/-) mice, but not in the eosinophil-deficient del-dbl-GATA strain. In contrast to Gr1+ neutrophils, which express both cross-reacting antigens Ly6C and Ly6G, SiglecF+Gr1hi eosinophils from allergen-challenged lung tissue are uniquely Ly6G+. While indistinguishable from the more numerous SiglecF+Gr1- eosinophils under light microscopy, FACS-isolated populations revealed prominent differences in cytokine contents. The lymphocyte-targeting cytokines CXCL13 and IL-27 were identified only in the SiglecF+Gr1hi eosinophil population (at 3.9 and 4.8 pg per 106 cells, respectively), as was the prominent proinflammatory mediator IL-13 (72 pg per 106 cells). Interestingly, bone marrow derived-(SiglecF+) cultured eosinophils include a more substantial Gr1+ subpopulation (50%); Gr1+ bmEos includes primarily a single Ly6C+ and a smaller double-positive (Ly6C+Ly6G+) population. Taken together, our findings characterize a distinct SiglecF+Gr1hi eosinophil subset in lungs of allergen-challenged wild-type and granule-protein deficient mice. SiglecF+Gr1hi eosinophils from wild-type mice maintain a distinct subset of cytokines, including those active on B and T lymphocytes. These cytokines may facilitate eosinophil-mediated immunomodulatory responses in the allergen-challenged lung as well as in other distinct microenvironments. (Percopo CM et al. 2016. J. Leukoc. Biol., in press) Other publications in this cycle include the invited commentary-review, Eosinophils, Galectins and a Reason to Breathe (Rosenberg, Druey 2016. Proc. Natl. Acad. Sci., USA, in press) which discusses the role of the carbohydrate binding galectins in eosinophil biology and asthma, and our invited review, Eosinophils, Probiotics and the Microbiome (Rosenberg, Masterson, Furuta. 2016. J. Leukoc. Biol., in press) in which we examined the current understanding of the relationship between eosinophils, endogenous microbial flora, and probiotic bacteria, with the hopes of opening the doors to more interest and research in this field.